Stainless Steel Coil Tube — Fan Coil Unit (FCU) Heat Exchanger Series

Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for use in fan coil unit (Fan Coil Unit, FCU) heat exchangers and central air conditioning terminal systems. These coil tubes serve as the core heat transfer elements within HVAC (Heating, Ventilation, and Air Conditioning) end-unit devices, where they facilitate efficient thermal exchange between circulating refrigerant or chilled water and ambient air. The product is engineered to meet the demanding requirements of modern building climate control systems, offering superior corrosion resistance, thermal conductivity, and mechanical durability under continuous cyclic operation.

As a specialized component within the HVAC supply chain, the coil tube integrates seamlessly with intelligent controller systems that regulate airflow velocity, water valve actuation, and temperature setpoints — enabling precise energy management and occupant comfort optimization in commercial and industrial environments.

Material & Properties

The coil tubes are fabricated from high-grade austenitic stainless steel, selected for their exceptional combination of corrosion resistance, weldability, and thermal performance in aqueous and refrigerant environments.

Base Material: Austenitic stainless steel conforming to ASTM A269 / A270 and EN 10216-5 standards. Primary grades include 304 (UNS S30408) and 316L (UNS S31603), with 316L preferred for aggressive or marine environments due to its elevated molybdenum (Mo) content providing enhanced pitting and crevice corrosion resistance.
Chemical Composition (304 Grade): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%, Phosphorus (P) ≤ 0.045%, Sulfur (S) ≤ 0.030%.
Chemical Composition (316L Grade): Carbon (C) ≤ 0.03%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%, with trace titanium (Ti) stabilization optional.
Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C for 304 grade; 14.6 W/(m·K) for 316L grade — ensuring efficient heat transfer in compact heat exchanger geometries.
Operating Temperature Range: −196°C to +870°C (304); −196°C to +870°C (316L), covering the full spectrum of refrigerant and hot-water heating applications.
Surface Finish: Available in 2B (cold-rolled and annealed), No. 4 brushed, or electropolished (EP) finishes. Electropolished surfaces reduce bacterial adhesion and are preferred for hygienic and pharmaceutical HVAC applications.
Corrosion Resistance: Excellent resistance to atmospheric corrosion, acidic condensate, and chlorinated water; 316L grade provides superior resistance to chloride-induced pitting in coastal or industrial settings.

Specifications

Parameter	Specification	Standard / Tolerance
Outer Diameter (OD)	6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4")	±0.05 mm
Wall Thickness (WT)	0.50 mm – 1.50 mm	±0.025 mm
Coil Pitch (Center-to-Center Spacing)	7.0 mm – 12.0 mm (adjustable per heat exchanger design)	±0.10 mm
Tube Length per Row	300 mm – 1,200 mm (custom lengths available)	±0.5 mm
Number of Rows	2 – 6 rows (configurable)	—
Bend Radius (Minimum)	≥ 3 × OD (to prevent wall thinning and ovality)	—
Maximum Working Pressure	1.6 MPa (standard); 2.5 MPa (heavy-duty)	Hydrostatic test at 1.5 × working pressure
Refrigerant Compatibility	R-410A, R-32, R-134a, R-407C, water/glycol mixtures	—
Flow Velocity (Nominal)	1.5 – 3.0 m/s (optimized for heat transfer coefficient)	—
Heat Transfer Efficiency (U-value)	250 – 450 W/(m²·K) depending on configuration	ASTM F2020 test methodology
Surface Roughness (Ra)	≤ 0.4 μm (electropolished); ≤ 0.8 μm (2B finish)	ISO 4287
Standards Compliance	ASTM A269/A270, EN 10216-5, GB/T 14976, ASME B31.5	—

Manufacturing Process

The production of precision stainless steel coil tubes follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and performance reliability:

Raw Material Selection & Verification: Stainless steel strip or tube blanks are sourced from certified mills and subjected to spectrographic analysis (Optical Emission Spectrometry, OES) to verify chemical composition compliance with the specified grade. Mill test certificates (Mill Test Report, MTR) are retained for traceability.
Coil Winding / Forming: Straight tubes are formed into helical coil configurations using CNC-controlled tube coiling machinery. The coiling process employs precision tooling and tension control to maintain uniform coil pitch and minimize residual stress. For fan coil unit heat exchangers, the tubes are typically formed into serpentine (hairpin) or continuous helical patterns depending on the exchanger design.
Welding: Where tube connections are required (e.g., at headers or manifolds), automated orbital welding or TIG (Tungsten Inert Gas) welding is employed. The weld seam is protected by a high-purity argon (Ar) gas shield (≥ 99.99% purity) to prevent oxidation. Weld quality is verified through visual inspection and, where specified, radiographic testing (RT) or ultrasonic testing (UT) in accordance with ASME Section IX.
Heat Treatment / Solution Annealing: Following forming and welding, tubes undergo solution annealing at 1,050–1,150°C followed by controlled cooling (air or water quench) to restore full austenitic microstructure, eliminate residual stresses, and maximize corrosion resistance. This step is critical for preventing sensitization and intergranular corrosion.
Pickling & Passivation: The annealed tubes are subjected to acid pickling (typically a mixture of nitric acid HNO₃ and hydrofluoric acid HF) to remove oxide scale, followed by passivation treatment to form a stable chromium oxide (Cr₂O₃) passive film on the surface. This enhances long-term corrosion resistance.
Surface Finishing: Optional electropolishing is performed using a controlled electrolytic process (typically 10–15% H₂SO₄ + 80–85% H₃PO₄) to achieve ultra-smooth surface roughness (Ra ≤ 0.4 μm), which reduces fouling and improves hygienic performance.
Dimensional Inspection & Quality Control: Each batch undergoes comprehensive inspection including OD and wall thickness measurement (using ultrasonic thickness gauges or calibrated micrometers), coil pitch verification, hydrostatic pressure testing, and dimensional conformity checks against the engineering drawing. Non-destructive testing (NDT) methods include magnetic particle inspection (MPI) for surface defects and dye penetrant inspection (DPI) for weld integrity.
Final Assembly & Packaging: Verified coil tube assemblies are cleaned, protected with corrosion-inhibitive packaging, and shipped with accompanying documentation including certificates of conformance, material test reports, and dimensional inspection records.

Applications

The stainless steel coil tube is a critical component across a wide spectrum of HVAC and thermal management systems:

Fan Coil Units (FCUs): Primary application — the coil tube forms the heat exchange core within FCU terminal units, enabling precise temperature regulation in commercial offices, hotels, hospitals, and residential buildings. Integration with intelligent controllers allows modulation of water flow and fan speed for energy-efficient operation.
Chilled Water & Hot Water Heating Systems: Used in air handling units (AHUs), unitary air conditioners (UACs), and radiant cooling/heating panels where the coil tube facilitates heat transfer between water circuits and air streams.
Refrigeration & Cryogenic Systems: Employed in evaporators and condensers where resistance to low-temperature refrigerants (R-410A, R-32) and thermal cycling fatigue is paramount.
Marine & Coastal HVAC: The 316L grade provides essential protection against saltwater-induced corrosion in marine air conditioning systems, offshore platforms, and coastal infrastructure.
Food Processing & Pharmaceutical Facilities: Electropolished coil tubes meet hygienic design requirements (3-A Sanitary Standards, EHEDG) for cleanroom HVAC systems where contamination control is critical.
Industrial Process Cooling: Used in specialized heat exchangers for chemical processing, electronics cooling, and data center thermal management where corrosion-resistant, long-life heat transfer components are required.

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product reliability and regulatory compliance:

ISO 9001:2015 — Quality Management Systems certification, demonstrating adherence to internationally recognized quality management principles covering design, production, inspection, and delivery.
ISO 14001:2015 — Environmental Management Systems certification, reflecting the company's commitment to sustainable manufacturing practices and environmental stewardship.
ISO 45001:2018 — Occupational Health and Safety Management Systems certification, ensuring safe working conditions and risk mitigation throughout the production process.
CE Marking (EU Conformity) — Products comply with relevant European Union directives including the Pressure Equipment Directive (PED 2014/68/EU) where applicable, ensuring market access and safety compliance in European markets.
ASME Certification — Manufacturing processes and weld procedures conform to American Society of Mechanical Engineers (ASME) standards, including ASME B31.5 (Process Piping) and ASME Section IX (Welding Qualifications).
EN 10204 Type 3.1 Test Certificates — Independent third-party inspection and material certification for each production batch, providing full traceability and compliance verification.
RoHS & REACH Compliance — Products are free from restricted hazardous substances in accordance with European Union regulations, ensuring environmental and health safety.
Third-Party Testing: Regular verification by accredited laboratories (e.g., SGS, Bureau Veritas, TÜV) for mechanical properties, corrosion resistance (salt spray testing per ASTM B117), dimensional accuracy, and heat transfer performance.

Unique Selling Points

The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through several key differentiators:

Engineered for Intelligent HVAC Integration: Designed with dimensional tolerances and thermal characteristics optimized for compatibility with smart fan coil unit controllers, enabling precise modulation of heating and cooling capacity in response to real-time environmental sensor data and building management system (BMS) commands.
Superior Corrosion Resistance with Long Service Life: The selection of 304 and 316L austenitic stainless steel grades provides a service life exceeding 25 years under normal operating conditions — significantly outperforming conventional copper or carbon steel alternatives in corrosive environments, reducing total cost of ownership (TCO).
Precision Manufacturing for Optimal Heat Transfer: Tight dimensional tolerances (±0.05 mm OD, ±0.10 mm coil pitch) ensure uniform flow distribution and maximize the overall heat transfer coefficient (U-value), translating to higher energy efficiency and lower operating costs.
Hygienic and Food-Grade Options: Electropolished surface finishes with Ra ≤ 0.4 μm meet the stringent requirements of pharmaceutical, biotechnology, and food processing industries, eliminating harborage points for microbial growth.
Full Traceability & Documentation: Every production batch is accompanied by comprehensive documentation including material test reports, dimensional inspection records, and weld procedure qualifications, ensuring complete supply chain transparency and regulatory compliance.
Customizable Configurations: Flexible manufacturing capability allows customization of tube diameter, wall thickness, coil pitch, row count, and surface finish to meet specific project requirements and thermal design parameters.

Technical Notes

Proper installation and maintenance of the stainless steel coil tube heat exchanger assembly is essential for sustained performance. The following considerations should be observed:

Ensure water quality in closed-loop systems maintains conductivity below 500 μS/cm and pH between 6.5 and 8.5 to prevent scaling and corrosion.
Periodic descaling and flushing of the coil tube circuit is recommended at intervals not exceeding 12 months to maintain thermal efficiency.
Avoid welding or mechanical modification of installed coil tubes without re-annealing and passivation treatment to preserve metallurgical integrity.
When integrating with intelligent controller systems, verify that the coil tube's thermal mass and response time characteristics are properly calibrated within the controller's PID (Proportional-Integral-Derivative) control loop parameters.